1. Field of the Invention
The present invention relates generally to a window covering, and more particularly to a positioning device of a cordless window covering or a cellular shade.
2. Description of the Related Art
A conventional cordless window covering includes two rails and a valance with opposite ends connected to the rails. Two cords are provided to connect the rails to change vertical positions of the rails respectively, and therefore the valance is folded or unfolded.
In order to fasten the rails to the cords while they are moved to the desired vertical positions, a conventional way is providing two bores on each rail for the cords to pass through. These bores are not aligned with bores on the rails, through which the cords pass, so that the cords will be rested against sidewalls of the bores to generate frictions. The frictions are proportional to a weight of the valance. The frictions may hold the rails on the cords. It is easy to under that the structure and the strength of the rail would be worn out fast because of the bores and the pressures of the cords. An improved design is to provide two cord clamping devices on the rail to connect the cords. The cord clamping device can slow the wear out of the rails, however, the problem of cord wearing still exists. The worn cords will have difficulty to hold the rails.